In general, an image sensor, which is a semiconductor device converting an optical image into an electrical signal, is typically classified as a charge coupled device (CCD) or a complementary metal oxide silicon (CMOS) image sensor (CIS).
The CIS device according to the related art includes a photodiode region for receiving a light signal and converting it into an electrical signal, and a transistor region for processing the electrical signal.
Also, the CIS device typically needs one or more capacitors per pixel array.
However, according to the related art, the photodiode region, the transistor region, and the capacitor region are implemented on one wafer during the same fabrication process.
In this case, because the distance from a lens to the photodiode becomes large due to a back-end-of-the-line (BEOL) metal line formed on the transistor region and the capacitor, there is a great loss of the light signal entered into the photodiode region.
Also, according to the related art, because a process is simultaneously performed on the relatively large sized photodiode region and the very small transistor region, a difficulty in a lithography process occurs, which results in many defects occurring, and the photodiode region is attacked in a subsequent process forming a transistor, so that the CIS characteristics would be deteriorated.
Also, according to the related art, as the device becomes smaller using technologies below 90 nm and 65 nm, the size of the capacitor reduces and thus, it becomes more difficult to manufacture the capacitor with a desired capacitance.
Also, according to the related art, since a multi-layer metal line and a capacitor are manufactured together, the distance from a microlens to a photodiode is long, which can result in many problems in manufacturing the microlens.
Also, according to the related art, the transistor region and the capacitor coexist in one CIS device, which results in a region where all of the light incident cannot be absorbed but, rather, is lost.